blown alpine mrd m605 amp

I have an Alpine MRD-M605 amp that was wired up and working just fine for a few days. Today it worked up until the time I turned my truck off and when I turned it back on no more thump.

The blue LCD display on top just blinks on and off, and does not display any messages at all. I checked all connections, all are good, tested voltage with the multimeter, all is well up to the amp. So I took it apart. There does not appear to be any burnt smell, or bulging or leaking capacitors.

I did notice that one of the MOSFETS on the side had a leg that was broken, I am not sure if I broke it while taking it apart or if it damaged earlier today, however I soldiered it back together and retested the amp with no success.

Please let me know what would be the next step to check out on this amp.

What are the numbers that are on the transistor with the broken leg?   Pu that info at diyaudio also.  Ir will speed up the process there also.  I will be at work all day, Perry will be of more help to you today.

The transistor that had the broken leg that I soldered back together is IRF540N

Here is some different info I collected at the request of one of the diyaudio members:

On the MOSFETS which are on the sides of the amp where the power leads hook up part number IRF3205, my multimeter reads 0 ohms between legs 1 + 2, and 2 + 3, but reads high numbers on 1 + 3, on all of them.

On the MOSFETS which are on the side of the amp where the speaker output terminals are part number IRF540N, my multimeter reads various numbers on all leg combinations on all of them.

On the output transistors on what would be the front side of the amp, I have 5 transistors, 4 different ones and 1 duplicate one. The tests as follows:

FRH20A15:
Leg 1 + 3 = .1 ohm
Leg 1 + 2 = 1.5 ohm
Leg 2 + 3 = Various numbers all over 1 ohm

RF2001:
Leg 1 + 3 = .1 ohm
Leg 1 + 2 = 4 ohm
Leg 2 + 3 = 4 ohm

C3421:
Leg 1 + 3 = Various numbers all over 1 ohm
Leg 1 + 2 = Various numbers all over 1 ohm
Leg 2 + 3 = Various numbers all over 1 ohm

A1358:
Leg 1 + 3 = Various numbers all over 1 ohm
Leg 1 + 2 = Various numbers all over 1 ohm
Leg 2 + 3 = Various numbers all over 1 ohm

C3421:
Leg 1 + 3 = Various numbers all over 1 ohm
Leg 1 + 2 = Various numbers all over 1 ohm
Leg 2 + 3 = Various numbers all over 1 ohm

Do not pull the 3205s out of the board.  Unless you know they are bad.  If you do have to remove a transistor from the board, please follow these simple steps.  I know it goes against all that you think should happen, but trust me it will make it a lot easier for you.  Put as much solder as you can get on the 3 joints of the transistor to be removed.  Using a pair of needlenose or small pliers, grab the tab of the transistor.  Do not pull them out of the hole when the time comes, the pliers are only so you do not leave your fingerprints on the tab of the transistor.  It is going to get really really hot.  Once you have solder on all3 joints, lay your soldering iron  across all 3 joints, on the under side of the board.  Depending on the quality of your iron it may take 20 seconds to get all 3 joints molten.  Once they are all liquid, gently rock the transistor out of the board.  Once removed, now is the time to use the solder sucker or decoldering braid.  If you have to buy a solder sucker, purchase an EDSYN Soldapullt device.  If you have to buy a soldering iron buy a WELLER.  The extra solder makes it easier to get the part out.  It greatly reduces the chance of damaging the circuit board. 

Thank you for all that info, I have to run out of town today, so I wont be able to test today, but will check them as soon as I get back and let ya'll know how it went.

ok with the tester set on the buzzer function, the 3205's all switch as they should. When the tester leads are placed on a leg, it will beeep and then stop, meaning it switched, and switch legs, and again will beep then stop until i switch legs again, back and forth. So all (4) 3205's are switching ok.

The 540's if i touch leg 2 + 3 they will switch, much faster than the 3205's, its a very small fast blip on the buzzer. But all seem to switch consistently although two of them seem to be not as responsive as the rest, but do switch.

The single RF2001T2D switches just fine.

The single FRH20A15 switches just fine.



Here is a shot of the board, I have highlighted where the different banks of transistors are.

The red are the 540's
The yellow are the 3205's
The blue are as follows:
1:2SC3421
2:2SA1358
3:2SC3421
4:RF2001T2D
5:FRH20A15

You stated earlier that the leg was broken on one of the 540s.  Which leg was broken.  If it was the left most leg, (Top Leg in your picture)  that would be a problem.  If it was the left leg, remove that transistor and mount the amp back to the heat sink, place a single 10 amp fuse in only one fuse holder, power it back up and let me know what happens then.

OK will do, it was the 3rd one down from the top how it is pictured in this photo, and it would be the top leg on that transistor which is leg #1.

OK, just to make sure I understand correctly, I will remove the whole transistor completely from the board, remove both 30 amp fuses, and replace just one of them with a 10 amp fuse and power it up, please let me know if I got that right, I don't want to misunderstand and cause further damage.

Also I forgot to note above, that the transistors numbered in BLUE 1, 2, and 3 do not respond to the test I ran above with the tester. They do not appear to switch at all. I am not sure if they work differently or not.

roger that, will do. Ok going to remove the previously mentioned transistor, and remount it back in the case and attach the heat sink. Power up and report what happens. What should happen with a missing transistor?

One more question, if there are normally two 30 amp fuses, what is the purpose of removing both of them and only putting 1 10 amp fuse in its place?

I have a 15amp fuse handy, I would have to dig to find a 10 amp fuse, would that be ok to use for the test?

the leg broke right in the middle, so it was easy to repair, right where the bend is.

OK the posts did not remove like I would have liked them too, so since they would not budge, I just unsolder-ed the leg that i repaired and clipped the other two at the bend just like that one, so I could repair them all if needed. I am going to reassemble now and test with a 15amp fuse.

Did you add extra solder to all 3 joints of the transistor before attempting to remove it?

yes sir I sure did, and it still didn't come out so I cut the other two posts. I will test it in the morning as its now 11:23pm.

OK, I am sad to report, still a no go, same blank blinking display. Please let me know what I should check next.

Any other ideas to check?

I am still not able to find out what is blown on this amp. I honestly wish I could find someone local to my area who wouldn't charge me an arm and a leg to repair it as I am at a lose and rather upset that I took it out of the box and it worked fine for two days until it blew. Only problem is I bought it two years ago and just never had the chance to use it as I was deployed during the time so I can't return it.

Sorry that neither Perry or I can help you much with that amp.  Neither of us have ever seen one.  He did post a link for you to obtain the service manual, did you look into that?  If you buy the manual and take a high resolution picture of hte schematic diagram and mail it to him, he can probably help you with it.   I do not know where you are located, but if you are willing to ship it to me, he would be more than excited to look at it for you for a very reasonable rate just so he can have some info for the next broken one we hear of. 

I am in south florida if anyone is located in that area or knows anyone in that area, I would love to get it looked at. I would hate to ship it as the weight of it would end up being a good bit to ship back and forth.